( function () {
/**
 * Normal map shader
 * - compute normals from heightmap
 */

const NormalMapShader = {
  uniforms: {
    'heightMap': {
      value: null
    },
    'resolution': {
      value: new THREE.Vector2(512, 512)
    },
    'scale': {
      value: new THREE.Vector2(1, 1)
    },
    'height': {
      value: 0.05
    }
  },
  vertexShader:
  /* glsl */
  `

		varying vec2 vUv;

		void main() {

			vUv = uv;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}`,
  fragmentShader:
  /* glsl */
  `

		uniform float height;
		uniform vec2 resolution;
		uniform sampler2D heightMap;

		varying vec2 vUv;

		void main() {

			float val = texture2D( heightMap, vUv ).x;

			float valU = texture2D( heightMap, vUv + vec2( 1.0 / resolution.x, 0.0 ) ).x;
			float valV = texture2D( heightMap, vUv + vec2( 0.0, 1.0 / resolution.y ) ).x;

			gl_FragColor = vec4( ( 0.5 * normalize( vec3( val - valU, val - valV, height  ) ) + 0.5 ), 1.0 );

		}`
};

THREE.NormalMapShader = NormalMapShader;
} )();
